German published patent specification OS 24 64 400 discloses a process for the production of a yarn by winding of continuous filament yarns about staple fiber bands. The breaking stretch of the winding filament yarn is at least equal to the breaking stretch of the spun fibers. The strength elongation characteristic of the spun fibers and that of the winding filament yarn are to be attuned to one another in the sense that the initial modulus of the winding filament yarn is great and thereby in stretch stress of the filament yarn there is rapidly built up a sufficently high tension. This leads to filament yarns consisting of smooth fibers, which correspondingly leads to textile disadvantages. The strength factor of the winding filaments, therefore is very low, and therefore, they contribute little to the strength properties of the core/mantle yarn.
It is further known from German published patent specification OS 26 27 220 that endless threads (filament yarns) can be joined together with staple fibers (spinning fibers).
It has proved it hitherto was possible, to be sure, to attain an improvement of the textile properties of the filament yarn, but it was not possible to bring about any appreciable increase of the strength properties. It was not possible to bring the strength properties of the core thread in harmony with the strength properties of the spun fibers (staple fibers) in such a way that a summation takes place of the strength properties.
Attainment of core/mantle yarns with improved strength properties is the basic objective of this inventiion.